The present invention relates to a gas generator comprising an expansion chamber which adjoins the fuel chamber, is connected to the fuel chamber by means of openings and has filters for the emerging gas flow, a surrounding filter resting against the perforated outer housing wall and being held and supported by a partition which is a filter tube.
It is important in the case of gas generators to let the gas flow generated in the fuel chamber flow out of the openings in the outer wall of the housing as fast and as uniformly as possible for the purpose of filling up the air bag. In this case, the gas must be cooled and purified with respect to the particles contained in the gas flow.
For this purpose, the gas is first guided through a coarse-mesh filter and then through a fine-mesh filter resting against the outer housing wall (see German Patent Document 39 21 472 C1).
However, the fine-mesh filter, which extends down to the filter tube, does not absolutely and with its whole circumference rest against the outer wall of the housing. As a result, a portion of the gas escapes between the filter and the outer housing wall and is neither cooled nor filtered. A construction of the gas generator in which the filter is held by brackets which are punched out of the filter tube and bent does not satisfactorily solve the problem. This is because a sealing-off of the filter edge with respect to the outer wall of the housing makes sense only if it is effective along the entire circumference.
An object of the present invention is to provide a solution which avoids the above-mentioned disadvantages and achieves an effective filtering and purifying of the gas flow with respect to particles.
This and other objects are achieved by the present invention which provides a gas generator that has a perforated outer housing wall, a fuel chamber, an expansion chamber which adjoins the fuel chamber and is connected to the fuel chamber via openings, includes a surrounding filter resting against the outer housing wall. A filter tube holds and supports the filter. A ring-shaped clamping device is provided between the filter tube and the edge of the filter. The clamping device presses the edge of the filter against the outer housing wall.
With the present invention, a number of advantages are achieved. The ring-shaped clamping device seals off the edge of the filter facing the gas flow uniformly along the entire circumference with respect to the outer wall of the housing and holds it in its installed position. In the lower area, the filter is protected from local thermal overstressing by the gas flow flowing through the filter tube openings.
The preassembly of the clamping device is very simple. The ring-shaped clamping device is placed on the filter tube; when it is pressed on, it is automatically centered and fixed by means of the small supporting legs mounted on the inner edge.
In contrast to the previously known construction, the filter of the present invention may have a shorter design, whereby a cost advantage is achieved which outweighs the manufacturing costs of the clamping device. A slag trapping groove provided on the interior edge of the clamping device clearly reduces the proportion of fine and coarse particles in the gas flow and, as a result of the swirling-together of the gas, causes a more effective utilization of the filter entry area. On the whole, by means of the use of the clamping device, there is less reduction in the power of the gas generator than the use of customary methods for the filtering-out of particles.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.